Optimization of Cassava (Manihot esculenta Crantz.) Fermentation Processes for Food-Secured Twenty-First Century Africa

Abstract

In mid-2021, Africa’s population was more than one billion three hundred and seventy million persons and this figure is expected to reach 2.5 billion people by 2050. On the basis of regional population, Eastern, Middle and Western Africa countries are bound to continue to experience rapid rates of population growth in the coming decades. Between 1960 and 2010, the urban population of Africa increased by a factor of 8. Based on 2018 United Nation’s projection, nearly 60% of African people will be living in urban areas by 2050. Of deep concerns are most Eastern, Middle, and Western African countries which will have their urban populations multiplied by a factor of 3 to 7. Similarly, the number of youth entering the labor force, as well as elderly, will continue to grow rapidly. The dramatic increase for food secured Africa occasioned by the sprawling African population, and the corresponding jobs required will be the biggest challenge most African countries will need to confront between now and 2050.The biggest challenges in this respect will be in Eastern, Middle and Western Africa where the number of youth will triple in the next 30 years. Currently, different cassava fermented products are staples in various countries of Africa. Specifically, in the past six decades, cassava has become a food security crop in sub-Saharan Africa (SSA) due to many favorable reasons. Many of these African cassava fermented products are still traditionally produced by spontaneous fermentation making the quality and safety of products uncontrollable, in addition to their incapability of mass production. Modern techniques have taken fermentation beyond preservation such that production is optimized via starter culture fermentation. These are done with a view of generating desirable organoleptic properties with quality and safety in mind. Beside this, a shift from traditional to industrial processing of cassava fermented products will generate jobs and provide enough food that will be needed to feed the projected highly urbanized future Africa. This paper advocates for the urgent need for optimization of cassava fermentation processes in Africa. However, such optimization should be characterized with multiple cultures fermentation which will generate desirable organoleptic properties, nutrition, quality and safety. Additionally, the wealth of information from genomics and proteomic era should be harnessed for improved culture performance and activities so as to improve the safety, quality and nutrient composition of cassava fermented food products indigenous to Africa. The possible impacts of such shift on food security in the twenty-first century Africa, realization of inclusive growth, poverty reduction, and achievement of economic convergence are going to be huge. It is therefore imperative for various African governments and policymakers to integrate this suggested shift into their future developmental plans so as to avoid the impeding ‘demographic time-bomb’.

1. Introduction

In mid-2021, Africa’s population was more than one billion three hundred and seventy million persons and this figure is expected to reach 2.5 billion people by 2050 [1]. The drivers for the rapid African population growth include high level of youthfulness of the population of most countries, high fertility levels, and high urban population growth [2]. On the basis of regional population, Eastern, Middle and Western Africa countries are bound to continue to experience rapid rates of population growth in the coming decades. However, the Northern and Southern Africa’s share of the total African population will decrease from 21–13% and 6–3% respectively by 2050 [2].

The urban population of Africa increased by a factor of 8 between 1960 and 2010 [3]. Based on 2018 United Nation’s projection, about 59% of African people will be living in urban areas by 2050 [4]. Guengant and May [2] submitted that Africa’s rapid urbanization resulted in 50 cities with more than a million inhabitants and two mega cities (Cairo, 11 million and Lagos, 10.8 million) in 2010. However, these authors further estimated that in 2030 there will be four mega-cities and 11 cities of 5–10 million inhabitants on African continent while 15 mega-cities and 20 cities with a population between 5 and 10 million people are highly probable by 2050. As per the projected increase in Africa’s urbanization rate, of deep concerns are most Eastern, Middle, and Western African countries which will have their urban populations multiplied by a factor of between 3 and 7.

Presently, a phenomenon known as “youth bulge” is a common experience in most African countries whereby youth aged 15–29 represent over 40% of the adult population. The attendant implication of this is that the number of youth entering the labor force will continue to grow rapidly between now and 2050. In 2010, the African and sub-Saharan Africa working age population aged 20–64 were estimated at 466 and 353 million respectively. However, it will reach 774 and 616 million respectively by 2030. By 2050, the number of 20–64 years old Africans will reach 1.097 billion. The implication of these is that between 2010 and 2050 a huge increase of labour force of 2.4–2.7 times the 2010 number will be witnessed [2]. The biggest challenge in this respect will be in Eastern, Middle and Western Africa countries where the number of youth will triple in the next 30 years. African demographic projection of the elderly up till 2050 has not been favorable as well. Almost all African countries are projected to experience dramatic increases of their elderly populations. The number of persons aged 65 years and more was estimated at 36 million in 2010. This number is expected to double and quadruple by 2030 and 2050 respectively.

Given the foregoing demographic analysis, it will be difficult to imagine the magnitude of the problems that will be associated with the sprawling African population, increasing urbanization rates, increasing “youth bulge” and the corresponding jobs required, and increasing elderly population by 2050. The dramatic increase for food secured Africa will most probably be the biggest challenge most African countries will need to confront between now and 2050.The biggest challenges in this respect will be in Eastern, Middle and Western Africa countries.

Various African countries are in different stages of demographic/fertility transition [2]. A total of 13 countries (all Southern and Northern Africa as well as island countries), accounting for 22% of the total population of the continent have completed their transition. In 41 countries, transition is still far from completion; where it ranged from “in progress transition” to “slow and irregular transition” and “very slow and/or incipient transition”. Overall, 31 countries, accounting for nearly 60% of the population of the continent and 70% of the sub-Saharan Africa population can be considered as being far from completing their transition. Demographic transition is usually accompanied by epidemiological transition, i.e., a shift in health patterns from communicable to non-communicable diseases [5]. In addition, socioeconomic changes are also associated with such transition whereby the economy shifts gradually from agricultural to industrial production and eventually to a service-based economy.

The onus for a food-secured twenty-first century Africa coupled with the realization of inclusive growth, poverty reduction, and achievement of economic convergence now squarely lays on various African governments and policymakers to design future developmental plans so as to avoid the impeding ‘demographic time-bomb’. In this regard, this paper advocates for the urgent need for optimization of cassava fermentation processes in Africa towards a food-secured and economically prosperous twenty-first century Africa.

2. Cassava: Africa’s super crop

The Portuguese traders from Brazil introduced Cassava (Manihot esculenta Crantz) to sub-Saharan Africa (SSA) in the sixteenth century [6]. The crop is now produced in 40 of the 53 countries of Africa, stretching through a wide belt from Madagascar in the Southeast to Senegal and to Cape Verde in the Northwest. Current statistics indicate that African countries account for 64% of the global production of cassava and five of them are among the top 10 largest global producers. In the lead is Nigeria, who is the largest producer of cassava in the world, representing 19.4% of the global production [7].

Cassava is cultivated under a wide range of ecological and agronomic conditions of SSA. It is adaptable to relatively marginal soils and erratic rainfall conditions. It gives high productivity per unit of land and labour. The certainty of obtaining some yield even under the most adverse conditions and the possibility of maintaining continuity of supply throughout the year make the crop very adaptable to rain-fed agriculture conditions [6]. Further to these, in the future, cassava has the potential to become a promising crop that can adapt to changing climatic patterns due to its low water and soil acidity requirement compared to rice [8, 9]. The global Agro climatic suitability map for cassava under rain-fed conditions and low level of inputs is shown in Figure 1. Given the state of Agricultural development in Africa, majority of crop cultivation are done under rain-fed conditions and low level of inputs and it is not surprising that these scenarios translate very well to a greater portions of SSA being suitable for cassava production. It was stated earlier that the biggest challenge of impeding ‘demographic time-bomb’ in Africa is in the Eastern, Middle and Western Africa countries. Interestingly, these regions are also the best suited regions in Africa for cassava cultivation as shown in Figure 1. It then behooves the concerned African leaders to consider cassava as a key driver for food security both now and in the future Africa.

Figure 1.

Agro climatic suitability map for cassava under rain fed conditions [10].

Currently, in most African countries and cultures, cassava has become a staple crop of choice [11] as the majority of cassava tubers produced is consumed locally as traditional fermented/unfermented meals, thus making cassava an important crop by production and consumption. Cassava tuber is fermented to produce a range of different products in Africa. Among these are garri, fufu, lafun, kokonte, agbelima, akyeke, beer, cossettes, chikwangue, kanyanga, attieke, mapanga, kivunde, Kondugbala and makopa. In Asia the fermented products produced from cassava are peuyeum, pancakes, tapai/tapey singkong, rondho royal/monyos and cake tape [12, 13, 14, 15]. Cassava is processed by a variety of methods depending on locally available processing resources, local customs and preferences. Nweke [16] reported that the five common groups of cassava products in SSA are fresh root, dried roots, pasty products, granulated products and cassava leaves.

In most SSA countries, cassava has established itself as a food security crop in the past six decades. For instance, total cassava consumption more than doubled in Africa from 24 million tonnes per year in the early 1960s to 58 million tonnes per year in the late 1990s. This large increase was due to a significant increase in per capita consumption in countries such as Ghana and Nigeria where cassava is produced as a cash crop for urban consumption. Cassava roots were the single largest source of calories in seven African countries (Angola, the Central African Republic, the Congo, the People’s Republic of Congo, Ghana, Mozambique and Nigeria) having 40 percent of the population in the late 1990s, contributing an average of nearly 600 calories per person per day [16]. In a similar development, it was the second largest source of calories in another 11 countries (the Republic of Benin, Cameroon, Côte d’lvoire, Guinea, Liberia, Madagascar, Sierra Leone, Tanzania, Togo, Uganda and Zambia.) with about 25 percent of Africa’s population, where it provided more than 300 calories per person per day. However, statistics from specific country indicate that many families in Congo ate cassava for breakfast, lunch and dinner thus contributing over 1000 calories per person per day or about 55 percent of the average daily calorie intake in the late 1990s [16]. It is worth mentioning that the significant contribution of cassava to SSA diets has not waned in the recent time. Detailed country data by agro-ecological zones indicates that cassava currently contributes 10–30% and 2–10% of calorie and protein supplies respectively in the diet of SSA countries in humid tropics, moist savanna, and mid-altitude regions [6, 17].

Beyond food security, cassava can potentiate a radical increase of value offering and trade status in its producing regions with a concomitant positive ripple effect on the entire economy of Africa. For instance, a study conducted in cassava growing SSA countries indicated that about 26% of cash income from all food crops in cassava-growing households was derived from sale of cassava [6]. These authors further reported that some SSA countries (Ghana and Uganda) are already taking advantage of inadequacies of Asian Exporters to satisfy the European Union market’s need in relation to cassava chips. There are also some import substitution possibilities for cassava flour and industrial starch in some SSA countries.

It is on record that between year 2001 and 2007, a Presidential Cassava Initiative (PCI) project was executed in cassava-producing countries in some selected SSA countries (Nigeria, Ghana, and the Democratic Republic of Congo). The project aimed at generating about 5 billion dollars annually from exporting value-added cassava products in addition to (1) enhancing the productivity and production of cassava by increasing the area cultivated to 5 million ha, with the hope of harvesting 150 million tonnes of fresh cassava tubers annually; (2) producing 37.5 million tonnes of processed cassava products for the local and export markets [18]. A subsequent, exploratory study by [19] showed that through the PCI, the Federal Government of Nigeria created a policy measure that supported the industrialization of cassava such as 10% cassava bread, 10% bioethanol in gasoline and replacement of paraffin with ethanol gel fuel as a cooking fuel. Furthermore, there were increased investment and employment in the cassava subsector; reduction of food import bills of Nigeria; and increased cassava yield from 10.8 to 20 t/ha. Similarly, [20] submitted that PCI did not only promote cassava production, but had spillover effects on both national food production and food security.

Guengant and May [2] had submitted that the number of youth will triple in Eastern, Middle and Western Africa countries between 2010 and 2050. Beyond the quest for providing food for this teeming population, there is also a need for realization of inclusive growth, poverty reduction, and achievement of economic convergence. Given that these three regions of Africa that are of deep concern incidentally constitutes the best region in Africa which is most suitable for cassava cultivation (Figure 1), it is high time the policy makers in these African regions evolve cassava developmental plans that will seek to exploit the food security and socio-economic potentials that are inherent in cassava value chain.

3. Traditional processing of some cassava fermented products in Africa

Cassava (M. esculenta) is a plant material that is mainly processed by fermentation. It is mostly a tropical crop, but has some similarities with potato in the methods of preparation, the inedible starchy state when fresh and bland flavor when cooked. It is a food security crop in the developing world [21]. However, the main challenges faced by processors using fresh cassava root are its bulkiness and short shelf-life. It deteriorates within 3–4 days of harvest resulting in high post-harvest losses of cassava [22]. Therefore, cassava is often processed into dried forms, mostly after fermentation. When the moisture content and water activity is lowered, it becomes durable and is shelf-stable [23]. This drought-resistant roots are fermented to produce a range of different products (Figure 2) which include gari, fufu, attoupkou, lafun, kokonte, ubuswage, agbelima, akyeke, cossettes, imikembe, chikwangue, kanyanga, ikivunde, attieke, inyange, mapanga, kivunde, kondugbala, meduame-m-bong, makopa, and dumby in Africa [12, 14, 24, 25].

Figure 2.

Selected fermented cassava products: (a) gari (forfoeghgari 1.blog); (b) fufu (nigeriagalleria.com); (c) attieke (gastronomieafricaine.wordpress.com); (d) lafun (madamsabi.com); and (e) agbelima (bergamini.be).

The fermented cassava products in Africa are produced by traditional methods that exploit mixed cultures of various microorganisms and in a domestic setting with only a few small and medium scale industrial operations [25]. The techniques used are usually laborious and time consuming. Typically, such production utilize spontaneous fermentation with no implementation of good manufacturing practice (GMP) and hazard analysis and critical control point (HACCP) plans. Thus, traditional methods of processing cassava roots can result in poor and varied quality products that contain unacceptable levels of cyanide and spoilage organisms [23]. This variation in quality occurs due to initiation of fermentation by prominent microflora from the raw material, environment and water that vary according to place and time of production [12].

3.1 Gari

About 70 percent of cassava is turned into gari [24] and consumed by around 200 million people [26]. It is consumed mainly in West, Central and East Africa [24]. Gari is produced by solid state fermentation to form dry, crispy, creamy-white granular product. It is made by fermenting and roasting mash produced from crushed cassava roots.

The traditional gari processing combines different stages of activity. Fresh roots are peeled, grated into pulps, and put in jute sacks for hydraulic pressing and fermentation. Some local producers use heavy stones in the place of a hydraulic jack between wooden platforms. The pulps are left in this state for 3 to 4 days, although some producers prefer a day or 2 days of solid state fermentation. It is during this stage that acidic taste is imparted to the final product [27]. Then a dewatered and fermented pulp are produced in form of lumps that are then crushed by hand. The fibers are separated from the fine pulp by sifting through a traditional sieve. The resulting small pieces are called grits which are roasted in reasonable portions using a wide frying pan with firewood as an energy source until they become dry and crispy. The processors who are mainly women are constantly in contact with smoke, heat, fume, and cyanide which affect their health over a long exposure period [28].

3.2 Lafun, cossettes, kanyanga, mapanga, and makopa

Fresh cassava roots are processed into fermented dried pulp or flour with same procedures in some African countries. The product is called lafun (Nigeria), cossettes (Democratic Republic of the Congo and Rwanda), kanyanga and mapanga (Malawi), and makopa (Tanzania). Cassava is cut into small pieces, washed, steeped in water for 3 to 4 days, drained, sun-dried and milled into powder (flour) (Figure 3). The characteristics of the finished products depend, to a large extent, on whether cassava roots are peeled or not before steeping in water; and whether the fermentation water is changed at intervals during fermentation [29].

Figure 3.

Flow diagrams of the production of some fermented cassava products at ambient temperature.

Many traditional processors adopted a minimum of 72 h fermentation of cassava. Although they do not know the advantage of longer fermentation time, the 3-day fermentation period helps to reduce cyanogenic glucoside to a reasonable level. [30] noted that dietary cyanogen results in tropical ataxic neuropathy (TAN), diabetes mellitus, and can aggravate iodine deficiency disorders (IDDs). The stages of steeping and drying during traditional lafun production are typically in an unhygienic earthenware or polyethylene vessels, or rusty drums (Figure 4). Sun-drying the fermented cassava mash could take up to 2 weeks, depending on the weather, making the control of drying conditions very difficult [31].

Figure 4.

Lafun steeping and drying stages; a and c show steeping conditions; b and d are different drying sites adapted from [23].

There is no formal standard or quality control on this traditional processing method (Figure 5). That is, there is no code of hygiene, food safety or nutrition standards during production. The processors are mainly farmers. So, they harvest cassava roots, process close to the point of harvest, and sell to consumers directly or to retailers. This lack of control indicates that traditional processing of cassava has challenges associated with quality and safety. Unfortunately, it is difficult to get reliable data on the scale of what the problem of the lack of regulatory might be [23]. The fermented dried pulp of cassava is usually ground into flour to be used for the processing of secondary products, such as stiff porridge (oka), doughnuts, and cake. The stiff porridge is obtained when the fermented cassava flour is stirred in boiling water [32], while doughnuts and cake are gotten from frying dough made with dried pulp mixed with wheat flour [24].

Figure 5.

Lafun processing environment adapted from [23].

3.3 Fufu

Fufu (called Foo-Foo in Central Africa) is a staple in both Central and West Africa. It is produced largely by solid-state fermentation where the cassava is not steeped in water but allowed to ferment in a solid-state under a hydraulic press [23]. Hence, the preliminary operations are similar to that of gari. Traditional production involves peeling, washing, and cutting cassava roots into thick chunks then soaking in water contained in earthenware pots or in a slow flowing stream. The roots are left to ferment for 3 to 4 days during which they become very soft (called mash) and produce a characteristic flavor of a retted cassava product [33]. The mash is subsequently sieved after fermentation, allowed to settle within 4 h. The sediment can then be processed by cooking in boiling water [34]. Another processing method is to expel excess water from the sediment by applying heavy pressure, roll it into balls, cook it in boiling water, and pound it to a smooth paste. Fufu is a wet fermented pulp and mostly marketed in this form. Recent work on fufu is geared towards producing it in a dry form to increase shelf-stability, availability and easy transportation [35].

3.4 Kivunde

Kivunde is a fermented cassava product made by heaping roots together for fermentation. It is referred to as bada in Tanzanian, and inyange in Burundi. Traditionally, kivunde is produced by spontaneous fermentation or ‘back-slopping’ [36]. For the back-slopping fermentation, a percentage of liquor from a prior kivunde spontaneous fermentation is added to initiate the fermentation process. The traditional fermentation of cassava into kivunde was found to be dominated by molds of the genera Penicillium, Fusarium, Rhizopus, Cladosporium, Mucor, and Aspergillus [12]. The traditional methods of processing cassava roots into kivunde among other products have safety issues concerning high levels of some mycotoxins [36].

3.5 Agbelima

Agbelima is a cassava fermented dough indigenous to Ghana. It is a sourdough cassava meal traditionally produced by using kudeme; an inoculum derived also from cassava roots [37]. The roots are peeled, washed, and grated with a cassava mill. The grated pulp is inoculated with kudeme, and packed into polypropylene sacks to drain and ferment for 3 days. The fermented mash is pressed, crushed and steamed [38].

3.6 Attiéké

Attiéké is the main fermented food product in Côte d’Ivoire and forms a significant part of their diet [39]. It is currently consumed in many neighboring countries like Togo, Mali and Senegal [40]. It is produced traditionally by using three different inocula: Alladjan, Ebrié, and Adjoukrou, made from boiled cassava roots [41]. Cassava roots are peeled, washed, cut in pieces, and grated. While grating, the cassava mash is mixed with any of the traditional inocula and some milliliters of palm oil. The inoculated mash is left in a covered container overnight to ferment. Excess water is squeezed out of the mash before sun-drying. The resulting granules are processed by steaming to form attiéké [24].

4. Industrialization of cassava processing in Africa: issues, challenges, and prospect

Cassava (M. esculenta), a shrubby tuberous plant of the Euphorbiaceae family, had been cultivated mainly for its starchy roots [42]. As an essential staple in some parts of the world, it is called different names in diverse regions. Malaysia and India named it tapioca, Francophone countries call it manioc, and in Spanish America, it is yucca. In Nigeria, it is known as ege or gbaguda by the people in the southwest; karaza or doyar kudu in the north; igari in the south, iwa unene or imidaka in the south-south; akpu, jigbo or abacha in the southeast [43].

Cassava is an important raw material for the production of many staples in Africa. Both fermented and unfermented products are derived from cassava roots across the globe. The unfermented products are high quality cassava flour (HQCF), starch, snacks, and pastries among others [23]. These unfermented products are produced from cassava type categorized as ‘sweet cassava’ for its low cyanide content. Thus, the processing of sweet cassava for consumption only requires a simple food preparation. The bitter variety, however, must be processed by any form of fermentation methods to attain a cyanide level that is not toxic for consumption [44].

Indigenous processors use spontaneous fermentation and back-slopping mainly as their production methods. These methods of production have classic problems associated with inconsistent product and sensory qualities. The problems are due, in part, to the microflora of the production environment, the variety of cassava used, the drying method employed, processing equipment availability and hygiene of the production plant [12]. Researchers in Food Sciences have given a great attention to upgrading traditional processes so as to optimize products and thereby increase cassava utilization.

Nigeria, Bénin, and Sierra Leone have shown notable and varying degrees of success in cassava processing at commercial level. The introduction of machines for most unit operations of cassava processing resulted in good achievement of various cassava products in the three countries. Governments policy directed towards promoting cassava subsector encouraged both small and large-scale processing industries in many Africa countries. A good example was the Nigerian Government’s Cassava Initiative that started in 2001 [14]. Small- and medium-scale factories were established by some entrepreneurs to supply high-grade refined intermediate cassava products like cassava-based glucose syrup, starch and HQCF to big manufacturing industries, such as Nestlé Plc. and Cadbury. So, in Africa, the industrial utilization of cassava is not just emerging but increasing day by day. The roots have found uses in many industries processing feeds, paints, textiles, adhesives, and other chemicals [14].

Urbanization and population growth are the key factors driving the demand for cassava products in Africa. Howbeit, the commercialisation of the cassava subsector requires the inputs of responsive private sectors. The private sector inputs market in Africa is not well developed and hardly service the cassava farmers [45]. There are as much agronomic challenges as there are challenges to agro-processing. The lack of cassava stem multiplication and distribution system in Africa is a major constraint for the adoption of high yield varieties by farmers. Although medium-scale industries had been able to reduce the cassava labour bottleneck through certain mechanized technologies; cassava harvesting, peeling, and drying operations for quantity, quality, and standardized products still pose huge challenges. The chief constraint to the industrialization of cassava is perhaps the mode of drying. There is no key success to efficient dryers for mass production of cassava products at the moment. Therefore, drying process takes about 3–4 days with apparent loss in product quality [46]. Presently, high quality cassava flour processing industries in Nigeria are now leveraging on the influx of flash dryer. However, it is worth mentioning that the high initial capital expenditure for procurement, couple with the energy cost now remains a big challenge to widespread adoption of this technology.

Furthermore, there is need to separate the traditional food-oriented market from the new emerging market for industrially processed cassava. Most cassava roots grown in Africa is cultivated, processed, and traded through traditional market networks with little known about the market structure for industrial cassava [47]. Due to population growth and urbanization, there must be a paradigm shift in the traditional utilization of cassava to the opportunities in diversify cassava markets. The successful commercialization of cassava subsector also lies on the users and consumers response to the cassava transformation process for secondary product supply and new food development respectively. Other than the setback highlighted, cassava has great economical potential with its unique features as raw materials for various intermediate and final products. Improvement in cassava production and strategies for marketing products would greatly expand trade and income.

5. Food and nutrition security: Africa at a crossroad?

About two decades ago, Africa was described as a continent in crisis; as it was racked with hunger, poverty and the HIV/AIDS pandemic. It was also the region with the fastest population growth, the most fragile natural resource base and the weakest set of agricultural research and extension institutions [16]. It is disheartening that a substantial shift from this narrative is yet to be attained about 20 years after. Current report indicates that Africa is home to 43 economies with the highest poverty rates in the world and yet is the youngest continent in the world as more than 400 million of its people are aged between 15 and 35 years old [48].

Good nutrition is pivotal to the achievement of several of the Sustainable Development Goals (SDGs) such as ending poverty (SDG 1), promoting gender equality (SDG 5), ensuring quality education (SDG 4), and reducing inequalities (SDG 10) [49]. Malnutrition (in all its forms) is due to a complex set of interacting factors, including the inadequate, unbalanced or excessive consumption of the macronutrients that provide dietary energy (carbohydrates, protein and fats) and micronutrients (vitamins and minerals) which are essential for physical and cognitive growth and development [50]. Multiple burden of malnutrition may exist in the form of undernutrition and micronutrient deficiencies, but in addition, overweight and obesity are emerging as significant health concerns in a number of countries.

Globally, the prevalence of undernutrition (PoU) has remained at 10.8 percent over 2017 and 2018. In 2018, there are 822 million undernourished people in the world, up from 812 million in 2017 and 797 million in 2016.Though it is on record that the prevalence of undernourishment in Africa fell from 24.5 percent in 2000 to 18.2 percent in 2014, but then started rising to 20 percent of the continent’s population, or 256 million people in 2018, with SSA having a share of 239 million undernourished people [50]. However, recent data indicates that Southern Asia and Sub-Saharan Africa respectively had PoU of 15.8 percent (257.3 million people) and 24.1 percent (234.7 million people) in 2019 [51]. In another development, out of the twenty countries affected with multiple micronutrient deficiencies globally, eighteen were from sub-Saharan Africa and two from Asia [52].

Undernutrition comes with considerable economic costs including lower cognitive skills and school attainment, and impaired physical development, which can reduce productivity in adulthood. Estimates from selected African countries (Egypt, Ethiopia, Swaziland and Uganda) indicate that productivity losses ascribed to adults, who suffered from stunting in their childhood, are huge. For example, annual losses of 3.7, 4.7, 0.092 and 0.899 billion US dollars, equivalent of 1.9, 16.5, 3.1 and 5.6% of GDP, have been estimated for Egypt, Ethiopia, Swaziland and Uganda respectively [53]. In recognition of the overwhelming economic burden of malnutrition, the WHO Member States in 2012 adopted a set of global nutrition targets. The six interlinked WHA global nutrition targets for 2025 are: achieving a 40 percent reduction in the number of children under 5 years who are stunted, achieving a 50 percent reduction of anemia in women of reproductive age, achieving a 30 percent reduction in low birth weight, ensuring that there is no increase in childhood overweight, increasing the rate of exclusive breastfeeding in the first 6 months up to at least 50 percent, and, reducing and maintaining childhood wasting to less than 5 percent. However, overall progress towards these WHA global nutrition targets remains unacceptably slow in Africa, as out of 54 African countries: 7 are on course to meet the target for stunting: 0 are on course to meet the target for anemia in women of reproductive age, 20 are on course to meet the target on overweight, 1 are on course to meet the target on exclusive breastfeeding, while 13 are on course to meet the target on wasting [50]. With these statistics, Africa is quite at a crossroad of food and nutrition insecurity.

In Africa, three major drivers of hunger and food insecurity are climate change, conflict and economic slowdowns and downturns [50]. In consideration of the fact that evolving coping strategies against the imminent consequences of climate change is more needed in Africa both now and in the nearest future, increased utilization of climate-smart crop is perhaps one of the needed approach to fight food and nutrition insecurity. In Africa, roots and tubers are one of the most consumed food groups and cassava as a climate-smart tuberous crop is an ideal crop to fight the scourge of malnutrition given its high rate of consumption by rural and urban Sub-Sahara African populations. Although cassava does not have a high nutritive value, especially for certain micronutrients and protein, the crop has benefitted from several initiatives focused on increasing its micronutrient load through biofortification. For instance, organizations like HarvestPlus have made great strides towards improving the nutritive value of cassava through the development of vitamin A-rich cassava and its promotion for adoption into the food systems of several African countries like Nigeria, Ghana, Cameroon, and DRC. In addition, food-to-food fortification using soybean flour/residue has the potential to produce cassava-based foods that could be used to fight macronutrient and micronutrient deficiencies in African countries where cassava products are staples [54, 55]. The onus therefore lays on African policy makers, especially in the Sub-Sahara Africa, to leverage on the potentials of value-added cassava-based products in addressing the twenty-first century food security concerns in Africa.

6. Optimization of cassava fermentation process: An imperative for twenty-first century food-secured Africa

As stated earlier, the dramatic increasing need for food secured Africa occasioned by the sprawling African population, and the corresponding jobs required, will be the biggest challenges most African countries will need to confront between now and 2050. In addition, the projected increase in urbanization rates and increased aged/elderly population are “demographic time bombs” that will further worsen food and nutrition security situation in most African countries in the coming decades if proactive steps are not taken to shift from traditional cottage level to mass scale food processing. While evolving future developmental plans so as to avoid this impeding ‘demographic time-bomb’, it is imperative for various African governments and policymakers to learn from European history, especially in relation to industrialization of food processing.

Food processing using fire and cooking has occurred since pre-historic times. However, more complex forms of food processing such as baking of bread, production of cheese, wine production, sun-dried or vinegar-pickled vegetables production, and salted or smoked meat production emerged in ancient and medieval times [56]. Historically, various factors are responsible for processing foods. These include impossibility to eat fresh food, seasonality of crop production, crop failures, wars and long sea voyages. However, the aims of modern processing are manifold, and include the prolongation of shelf-life, ensuring safety, improving palatability, increasing variety, improving nutritional value and increasing convenience [57]. Mass scale food processing (producing foods in large amounts) was introduced during the industrial revolution in the eighteenth and nineteenth century, starting with the advent of canned and pasteurized foods [56]. In the first half of the twentieth century, Europe was ravaged by malnutrition (undernutrition), caused by poverty, an economic depression and two catastrophic world wars [57, 58]. As a result, mass food production focused on sustaining the European population; reducing foodborne diseases, malnutrition and nutrient deficiencies by providing protein-rich, energy-dense and fortified foods (with vitamins) that were accessible to all [56].

It is important to envision the impact of the demographic projections for Africa up till 2050 on African food and nutrition security situation in the middle of this twenty-first century. This will be helpful to appraise the needed imperatives that must be factored in while evolving a sustainable food and nutrition security road map for Africa for the rest part of this century. Rapid population growth will demand more food to be produced using the same size of arable land. Desert encroachment and climate change and their accompanied consequences will constitute major problems for food production, except innovative ways of sustainable agricultural practices are adopted. Increase urbanization rates will limit availability and accessibility of traditionally produced food for the great majority that live in urban environment. Increased poverty rate, economic slowdown or downturn will definitely limit food accessibility of the poor majority. Most often than not, children, women and elderly are the most vulnerable groups whenever there is a food crisis. This scenario will definitely be sacrosanct amid the looming possible food crisis in Africa build up to 2050.

As stated earlier, the biggest challenges of impeding ‘demographic time-bomb’ in Africa is in the Eastern, Middle and Western Africa countries. Interestingly, these regions are also the best suited regions for cassava cultivation in Africa as shown in Figure 1. Kolapo and Sanni [59] submitted that utilization of locally sourced food material must be of primary consideration in the quest of any nutritional development programme. It then behooves the concerned African leaders to consider cassava as a key driver for food security both now and in the future Africa. This will be consistent with the earlier description of cassava as Africa’s super crop.

The cassava fermentation process varies from one region to another, both in Africa and other part of the globe. However, these fermentation techniques in cassava processing are broadly categorized into solid-state and submerged fermentation. In solid-state fermentation, cassava root is not soaked in water whereas in submerged fermentation processes, cassava roots are soaked in water for the duration of fermentation. Gari, Attieke, and Injera are produced by the former technique [60, 61, 62] while Fufu, Pupuru, and Chikwangue are produced using the later technique [63, 64, 65]. Microorganisms of various groups such as lactic acid bacteria (LAB), yeasts, molds and Bacillus strains, among many others, are involved in the fermentation of cassava-based foods indigenous to different parts of the world. The sources of these microorganisms are usually raw ingredients, the traditional utensils used for the processes, water used for the processing and the immediate atmosphere. Some genera/species of microorganisms that have been reported concerning various cassava fermented foods in Africa are stated in Table 1. During fermentation of cassava products, these microorganisms have been linked to the following roles: cyanide and antinutrients reduction, protein enrichment, food preservation, texture improvement, aroma and flavor change [66, 67, 68].

Food product	LAB and other bacteria	Yeasts	Molds	Countries of production
Gari	Bacillus subtilis; Bacillus coagulant; Bacillus species; Lactobacillus plantarum; Lactobacillus fermentum; Lactobacillus brevis; Lactobacillus pentosus; Lactobacillus acidophilus; Lactobacillus sp; Leuconostoc Alcaligenes; Leuconostoc fallax; Corynebacterium manihot; Corune bacterium species, Pseudomonas mesenteroides, Weissellapara mesenteroides; Corynebacterium; Bacteroides sp; Actinomyces sp	Saccharomyces fragilis; Saccharomyces cerevisiae; Saccharomyces rouxii; Geotrichum candidum		West, Central, and East Africa countries
Ikivunde	L. plantarum; L. brevis; L. fermentum; Leuconostoc mesenteroides	Geotrichum candidum		Burundi, Rwanda
Chikwangue	Lactococcus lactis; Leuconostoc sp; Lactococcus plantarum; L. plantarum; Clostridium spp.			Main central Africa countries
Inyanga			Aspergillus oryzae, A. fumigatus, Penicillium chrysogenum, Rhizopus stolonifera, Mucor spp	Burundi
Attieke	Lactobacillus plantarum; Lactobacillus; fermentum; Lactobacillus cellobiose; Lactobacillus brevis; Leuconostoc mesenteroides; Lactobacillus sp; Bacillus sp, Bacillus sphaericus; Bacillus brevis, Bacillus; coagulants, Enterococcus faecium	Candida krusei; Kloeckera japonica; Saccharomyces cerevisiae		Bénin, Mali, Sénégal, Togo
Fufu	Lactobacilluscallobiosus L.bulgaricus, L. brevis,L. plantarumLeuconostocmesenteroides	Candida famata		Nigeria
Pupuru	Lactobacillus plantarum Lactobacillus fermentum Cryptococcus humicola Leuconostoc spp. Corynebacterium pyrogenes	Geotrichum capitatum Candida famata Saccharomyces cerevisiae Geotricum candidum		South western Nigeria and west Africa

Table 1.

The main microorganisms associated with fermentation in some cassava-based food (Adapted from [66]).

The fermented cassava products in Africa are produced by traditional methods that exploit mixed cultures of various microorganisms and in a domestic setting with only a few small and medium scale industrial operations [25]. These traditional methods of processing cassava roots do result in poor and varied quality products that contain unacceptable levels of cyanide and spoilage organisms [23]. Though, the earliest production of cassava fermented foods was based on spontaneous fermentation due to the development of the microflora naturally present in the raw material, there are current attempts to optimize cassava fermentation processes using starter cultures. Padonou and co-workers [32] assessed the role of Saccharomyces cerevisiae 2Y48P22, Lactobacillus fermentum 2L48P21, Lactobacillus plantarum 1L48P35 and B. cereus 2B24P31 in root softening and the overall organoleptic quality of Lafun in a quest to develop a suitable starter culture for the standardized production of Lafun. Recently, [23] evaluated the impact of the developed starters (Weissella koreensis (2 strains), Lactococcus lactis and Leuconostoc mesenteroides), singly and in combination, on Lafun nutritional quality, rheological properties, volatile flavor profile, NMR metabolite profile, cyanide reduction and microbial load using three cassava varieties (Bitter: IBA30527; Fortified: IBA011371; and Sweet: TMEB117). In a related development, [69] investigated a possible nutritional enrichment of Lafun using Lactobacillus plantarum and Saccharomyces boulardii as starter microorganisms.

While developing starter cultures for gari fermentation, [26] recommended the inclusion of L. plantarum, L. fallax and Lactobacillus fermentum species in a mixed culture as starters for gari production because of their huge linamarase activity, fast acid production and production of antagonistic substances like bacteriocins and hydrogen peroxide. In addition, [70] submitted that these three species had a beneficial property of high sugar fermentation profile for indigestible stachyose and raffinose sugars. In another development, [71] evaluated the effect of L. plantarum strains in fufu production. The outcome of their study indicated that fufu, produced using L. plantarum as the starter culture, had more desirable pasting quality and flavor in comparison to the traditionally produced samples. Molds of the genera Penicillium, Cladosporium, Rhizopus, Mucor, Aspergillus and Fusarium were found to dominate the traditional fermentation of cassava into kivunde [12]. However, [36] reported that this traditional method has safety issues concerning high levels of some mycotoxins. Therefore, the potential of L. plantarum to improve the quality and safety of this product was demonstrated by [12]. Bouatenin and co-workers [72] used LAB strains (L. plantarum and L. mesenteroides) among other microbes as starters, both singly and in combination for attiéké production. They reported that acid production responsible for sourness and detoxification of the products was the job of LAB strains. Similarly, Agbelima, like attiéké, is a sourdough cassava meal in which souring was achieved by LAB such as L. mesenteroides, Lactobacillus brevis and L. plantarum [73].

Though these optimization attempts resulted in positive flavor, nutritional and physical properties and cyanide reduction, thereby advancing the development of these starter cultures and providing a basis for further research required for their development and adoption; there is still a long way to go in the industrialization of the production process of these Africa cassava fermented foods. It is incontrovertible that the application of molecular technologies with emphasis on the application of novel sequencing technologies to generate phylobiomes, metagenomes and metatranscriptomes for microbial community profiling that complement culturing studies has greatly facilitated monitoring of fermentation ecosystems and characterization of the microbial species in the past two decades. Such technologies involved the use of High-Throughput-Sequencing (HTS) techniques such as whole-genome sequencing, amplicon bases meta-taxonomic approaches (such as 16S rRNA sequencing), shotgun metagenomics, and (meta) transcriptomics, and rely on downstream bioinformatics analysis [74]. In this regard, an increasing number of fermented foods of Asian origin were analyzed with these techniques [75]. However, in Africa, whole-genome sequencing was initially used for the analysis and surveillance of foodborne pathogens [76].

While fermented food products around the world are increasingly being studied using shotgun metagenomic techniques, very few studies have explored the use of shotgun sequencing in African fermented foods, with some exceptions being “Nunu” (Ghana), “Kokonte” (Ghana/Togo) and “Wagashi” (Benin) [77]. Given that, shotgun metagenomic sequencing facilitates deeper insights into the microbiome, allowing strain-level identification, functional annotation including carbohydrate pathways and bioactive molecule production (such as bacteriocins), and the assembly of high quality genomes in the form of metagenome-assembled genomes (MAGs) [78, 79], there is an urgent need to harness the traditional culture-based and HTS techniques to characterize and optimize the microbiome of African cassava fermented foods, from commercial to nutritional and health-promoting aspects. This will require a huge investment on the part of the leaders of concerned African countries.

Most food fermentation processes depend on mixtures of microbes which act in concert to produce the desired product characteristics. Brenner and co-workers [80] posited that this can be explained by two features. First, members of the consortium communicate with one another by trading metabolites or by exchanging molecular signals. Second, division of labour exists between the members of the consortium leading to an overall output that can only be explained by combining tasks performed by constituent individuals or sub-populations. The best well-known example is the proto-cooperation between Streptococcus salivarius subsp. thermophiles and Lactobacillus delbrueckii subsp. bulgaricus in yogurt fermentation with clear links to product functionality [81]. Another example of proto-cooperation is the development of a highly efficient fermentation process using a co-culture of L. plantarum SM39, and Propionibacterium freudenreichii DF13 for folate and vitamin B12 production [82, 83]. In a recent alkaline fermentation of indigenous African fermented foods, [84, 85] documented the use of Bacillus subtilis LB3, Staphylococcus xylosus SAU3 and L. mesenteroides ssp. cremoris LAB5 for controlled fermentation of soybean-daddawa, in which the naturally fermented sensory attributes of soybean daddawa was nearly replicated in a controlled setting, thus holding a great promise for subsequent industrialization of soybean daddawa production. Given the foregoing scenarios, optimization of cassava fermented foods indigenous to Africa should be characterized with co-cultures fermentation which will generate desirable organoleptic, nutritional, quality, and safety properties.

While contemplating industrialization of cassava fermentation process in Africa, two possibilities that could be leveraged upon are backslopping (in the short term) and the use of functional starters (in the long term). Backslopping involves inoculation of the raw material with a small quantity of a previously performed successful fermentation, which eventually results in dominance of the best adapted strains. Functional starter cultures are starters that possess at least one inherent functional property which can contribute to food safety and/or offer one or more organoleptic, technological, nutritional, or health advantages [75]. Backslopping is still in use, for instance in the production of sauerkraut and sourdough, and particularly for products for which the microbial ecology and the precise role of successions in microbial population are not well known [86]. It also represents a cheap and reliable preservation method in less developed countries [87], whereas in Western countries the use of starter culture in large-scale production of fermented foods has become an important routine procedure of the food industry [88].

African leaders in 2013, through the 50th Anniversary Solemn Declaration during the commemoration of the Fiftieth Anniversary of the Organization of African Unity (OAU), while acknowledging past successes and challenges, rededicated themselves to the continent’s accelerated development and technological progress. They emphasized a guiding vision “to build an integrated, prosperous and peaceful Africa, driven and managed by its own citizens and representing a dynamic force in the international arena”, and forthwith identified seven aspirations to serve as pillars for the continent in the foreseeable future. Agenda 2063 was subsequently designed to translate these aspirations into concrete objectives, milestones, goals, targets and actions/measures. The first aspiration of the Agenda seeks to obtain prosperous Africa based on inclusive growth and sustainable development. The policy document defined a prosperous Africa as a continent with a high standard of living, quality of life and well-being; whose citizens are healthy and well-nourished, subsequent to a robust food and nutrition strategy initiatives. A prosperous Africa is also expected to be well educated and be a key player of knowledge economy and become a Science, Technology and Innovation hub. As a prosperous Africa, the continent is expected to adopt modern Agriculture for increased productivity and production. In order for Africa to attain prosperity status, it was envisioned that Africa must develop coping strategies against the imminent challenges of climate change. The sixth aspiration of Agenda 2063 envisions an Africa whose development is people-driven, relying on the potential of African people, especially its women, youth, and children. These are to be achieved by attainment of full gender equality in all spheres of life, as well as rigorous youth and children empowerment.

It is on record that African countries account for 64% of the global production of cassava and five of them are among the top 10 largest global producers [7]. Africa must therefore know what must be done to this ‘cassava resource’ to achieve economic prosperity as well as food and nutrition security, since utilization of locally sourced food material must be of primary consideration in the quest of any nutritional development programme [59]. The foregoing analysis encapsulated in this paper has clearly shown what must be done in this regard.

7. Conclusion

The biggest challenge of impeding ‘demographic time-bomb’ in Africa is in the Eastern, Middle and Western Africa countries. Interestingly, these regions are also the best suited regions for cassava cultivation in Africa It then behooves the concerned African leaders to consider cassava as a key driver for food security both now and in the future Africa. This is consistent with the earlier description of cassava as Africa’s super crop.

Demographic transition is usually accompanied by both epidemiological and socioeconomic changes whereby the economy shifts gradually from agricultural to industrial production and eventually to a service-based economy. Incidentally, 31 African countries, accounting for nearly 60% of the population of the continent and 70% of the sub-Saharan Africa population can be considered as being far from completing their transitions. The projected increase in population figures, urbanization rates and increased aged/elderly population are “demographic time bombs” that will further worsen food and nutrition security situation in most African countries in the coming decades if proactive steps are not taken to shift from traditional cottage level to mass scale food production and processing.

While evolving future developmental plans so as to avoid this impeding ‘demographic time-bomb’, it is imperative for various African governments and policymakers to learn from European history, especially in relation to industrialization of food processing. In the twentieth century, political, social, and economic changes, and scientific and technological advances moved at an ever increasing pace and impacted on the European food processing industry and influenced the ways foods were processed and marketed. As a result, mass food production focused on sustaining the European population; reducing foodborne diseases, malnutrition and nutrient deficiencies by providing protein-rich, energy-dense and fortified foods (with vitamins) that were accessible to all.

If Africa must contain the impending demography-associated food crisis in the coming decades, increased food production and industrialization of the processing of produced food crops is never an option but a necessity. As Africa’s super crop, cassava has a great role to play in this respect, as fermented cassava products have become prominent staples across many SSA countries. There is therefore an urgent need to harness the traditional culture-based and HTS techniques to characterize and optimize the microbiome of African cassava fermented foods, from commercial to nutritional and health-promoting aspects. This will require a huge investment on the part of the leaders of concerned African countries. However, given the immense benefits of such project and the expectations of Agenda 2063, African leaders must begin to put their resources where their mouths are so as to ensure that the twenty-first century Africa is food-secured.

Acknowledgments

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Conflict of interest

The authors declare no conflict of interest.